Generally, compressors are driven by some external prime mover such as an internal combustion engine or electric motor and supply compressed air to a receiver tank, from which the compressed air is drawn for usage by various pneumatic devices. Various compressor control apparatus has been proposed to regulate the output of the compressor, and the speed of the prime mover, in accordance with the demand for the compressed air. Generally, this control apparatus attempts to maintain the receiver tank pressure within a narrow range by loading and unloading the compressor and by regulating the speed of the prime mover, to match the demand for air. Small variations in pressure within the receiver tank are used to actuate valves which operate compressor unloading devices and motor speed devices.
Some prior art compressor control apparatus, such as those disclosed in U.S. Pat. Nos. 1,679,133, 1,906,012, 2,113,637, and 2,626,099, make no provision for utilizing the movement of one control member in one control circuit for automatically and simultaneously adjusting the speed of the prime mover and the functioning of the compression chambers. Nor is the prior art control apparatus arranged to bring in and take out compression chambers in succession one at a time to adjust compressor output in relation to air demands on the compressor to be able to operate the compressor efficiently at below-peak periods of air demand. Other prior art control apparatus utilize a first control circuit to operate the compressor unloading devices and a second control circuit to operate the driver speed devices. U.S. Pat. No. 2,585,168 is representative of this control apparatus. In control apparatus and systems of this type where two control circuits are utilized, cooperative interaction is required between the two circuits and independent settings and adjustments of either circuit are sometimes difficult to make.
Another prior art control system disclosed in U.S. Pat. No. 2,629,536 utilizes a speed control circuit that requires a governor to control the speed of the prime mover. This type of system is also difficult to adjust and requires additional costly components.
Accordingly, it is an object of the present invention to provide a simple, durable and efficient method and apparatus for controlling the operation of a compressor.
Another object of the present invention is to provide a novel and improved method and apparatus for controlling a compressor characterized by one control assembly responsive to air demand to adjust both speed and output capacity of the compressor to meet particular air demands with energy input to the compressor being closely matched to air demands so that proportionally less energy is required to operate the compressor during below-peak demand periods.
Yet another object of the present invention is to provide a novel and improved method and apparatus for controlling a compressor that provides a close regulation of receiver tank pressure over a wide range of compressed air demands.
A further object of the present invention is to provide a novel and improved method and apparatus for controlling a compressor having safety features whereby compressor output is rapidly decreased in the event of a gross air leakage and there is an automatic return of the apparatus to ambient pressure after a standard shut-down.
Still a further object of the present invention is to provide a novel and improved control assembly operatively associated with the speed control member of a prime mover with a plurality of compression chambers associated with the pressure-actuated unloader devices for the compression chambers with the movement of one directional control member simultaneously adjusting both the speed regulating member and a control valve, which in turn adjusts the unloader devices to successively bring in and take out one of a plurality of compression chambers one at a time in relation to compressed air demand on the compressor.